Data Link Communications
DTC U1000CIRCUIT DESCRIPTION
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the ID number of the module which sent the message for State of Health monitoring, Node Alive messages. When a critical operating parameter is not received, the module use a default value for that parameter. When a module does not associate an ID number with at least one critical parameter within about 5 seconds of beginning serial data communication, DTC U1000 is set. When more than one critical parameter does not have an ID number associated with it, the DTC will only be reported once. DTC U1000 will set as long as U1300, U1301, or U1305 do not have a current status.
The table list the modules on the class 2 serial data circuit that will set a U1000 and should be actively communicating the previously described messages on the class 2 serial data circuit.
CONDITIONS FOR RUNNING THE DTC
- The ignition switch run power mode is selected.
- The modules voltage supply is within normal operating value, approximately 9-16 volts.
CONDITIONS FOR SETTING THE DTC
At least one critical operating parameter has not been associated with a modules assigned ID number within about 5 seconds after beginning serial data communication.
ACTION TAKEN WHEN THE DTC SETS
- The SERVICE VEHICLE SOON indicator illuminates.
- The module will use default values for the missing parameters.
CONDITIONS FOR CLEARING THE DTC
- A current DTC will clear when all critical operating parameters for the module have been associated with an ID number, or at the end of the current ignition cycle.
- A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
DIAGNOSTIC AIDS
When a malfunction such as an open fuse to a module occurs while modules are communicating, a Loss of XXX Communication DTC is set as current where XXX is equal to the 3-digit module identification number. When the modules stop communicating, the ignition is turned OFF, the current Loss of XXX Communication DTC is cleared, but the history DTC remains. When the modules begin to communicate again, the ignition is turned ON, the module with the open fuse will not be learned by the other modules so U1000 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only U1000 is set. When this DTC sets, the module uses a default value for the missing parameter. A current DTC U1000 will clear when all of the critical operating parameters for the module have been associated with an identification number or when the current ignition cycle end. A history U1000 will clear upon executing 100 ignition RUN cycles with no recurrence of the malfunction.
TEST DESCRIPTION
Steps 1-6:
Steps 7-14:
Step 15:
The numbers below refer to the step numbers on the diagnostic table.
2. A DTC U1001-U1254 Lost Communications with XXX with a history status may indicate the cause of U1000.
3. The modules not communicating are the likely cause of U1000. The modules that are available on the class 2 serial data circuit are listed in the Circuit Description.
8. The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set DTC U1001-U1254 Lost Communications with XXX for those modules that it was monitoring.
10. The modules which can communicate indicate the module which can not communicate. You must clear the serial data communication DTCs from these modules to avoid future misdiagnosis.
13. If all modules are communicating, the module which set U1000 may have done so due to some other condition.
15. The module which set U1000 is the likely cause of the malfunction.